Nickel hydroxide is an important material in the manufacture of positive nickel electrodes of alkaline batteries. Doping the electrode's nickel hydroxide with suitable additives increases the nickel hydroxide's electrochemical activity. U.S. Pat. Nos. 4,844,999, Re. 34,752 and 5,366,831, all to Yuasa Battery Company, Limited of Japan document this and other beneficial properties obtained from doping. The common features of these processes include dissolving the additives' salts in a nickel feed solution and coprecipitating the additives with nickel hydroxide using a base. Generally, these processes rely on introducing sodium hydroxide to precipitate metal from their sulfates.
Inco Limited's U.S. Pat. Nos. 5,281,494 discloses a method of dissolving metal additives and coprecipitating these to dope nickel hydroxide. This process operates with an oxidizing potential at temperatures above 180.degree. C. These high temperature conditions yield a stable-crystalline product having diminished electrochemical performance in batteries. Similarly, U.S. Pat. No. 5,447,707, discloses a process that introduces additives directly from powder into nickel hydroxide. Unfortunately, this process introduces small quantities of nitrates into the nickel hydroxide.
The process described in the U.S. Pat. No. 5,545,392, produces nickel hydroxide with the direct conversion of elemental nickel into nickel hydroxide from a closed loop process. The introduction of additives, in the form of their salts, into the recycled feed solution or directly into a reactor is possible with this process. This process of introducing additives' salts however upsets the anion balance. Furthermore, this process requires: 1) bleeding a portion of the process liquor to restore the anion balance; and 2) subjecting this bleed stream to necessary treatments that would produce an environmentally acceptable effluent for disposal.
Oshitani et al.'s "Development of a Pasted Nickel Electrode with High Active Material Utilization" discloses battery's increased active mass utilization achieved from coating nickel hydroxide with a layer of cobalt hydroxide. In particular, the authors documented that nickel hydroxide's surface conductivity increased from 0.15 S/cm to 12.8 S/cm by coating it with cobalt oxyhydroxide. The charging cycles of nickel hydroxide-containing batteries converts CoO powder to Co(OH).sub.2 that precipitates on the nickel hydroxide. Eventually, the cobalt hydroxide oxidizes to a stable-cobalt oxyhydroxide coating during repeated charging.
It is an object of this invention to develop a method for incorporating additives into nickel hydroxide in a manner that does not over-crystallize the hydroxide or require the addition of salts to the system.
It is a further object of this invention to provide a pollution-free process for incorporating additives into nickel hydroxide.
It is a further object of the invention to develop a method for distributing additives, such as cobalt, between the nickel hydroxide's internal lattice or as a surface-rich layer that surrounds the nickel hydroxide particles.
It is a further object of this invention to provide a method for incorporating and coating cobalt-free nickel hydroxide with cobalt.